Statistical follies: "peak" cars in VT

UVM economist Art Woolf suggests 

Vermont may be on the declining side of a “peak cars” curve.

...and offers the following graph as evidence.
 

The problem is that simply looking at the number of registrations is misleading, because registrations are strongly associated with the size of the driving population.  This is noted in the title and article, but the author doesn't actually, you know, deal with it.  We're really interested in whether the typical Vermonter is more or less likely to own a car now than 10-20 years ago.   A more useful chart would look at the number of registrations, relative to the size of the driving population (say, by plotting the ratio of registrations to population on the vertical axis) over time. 

Moreover, the numbers in the bar chart in the article don't match the numbers from the census (the census is counting buses, but the census numbers are lower than Woolf's, so maybe Vermont has negative buses?).  And, of course, the article contains no references or (heaven forbid, because it's only 2013) links to the data source the author is using.

 

Using Census motor vehicle registration and population data, I see something more like:

1980	1985	1990	1995	2000	2001	2002	2003	2004	2005	2006	2007	2008	2009
347	398	462	492	515	534	537	516	523	508	588	565	581	557
511	530	563	589	609	612	615	617	618	619	620	620	621	622
0.68	0.75	0.82	0.84	0.85	0.87	0.87	0.84	0.85	0.82	0.95	0.91	0.94	0.9

 

the last row is the ratio of registrations to population, suggesting that the rate of vehicle ownership has increased over the last 30 years.  I'm a little suspicious (okay, a lot suspicious) of the enormous jump from 2005-2006, but have no experience with the data from which I can form a hypothesis, other than, "someone should check that out."